Corrosion resisting low alloy steel

ABSTRACT

Corrosion resisting low alloy steel having stress-corrosion cracking resistability, good weldability and higher strength under some kind of environment containing H2S and the like, which is chiefly composed of Cu-Cr-A1 system constituents without addition of strengthening elements such as Ti, Nb, V and the like.

United States Patent Masayuki Tanimura Yokohama-shl; Elhachiro Sunaml, Yokohama-shl; Toshio [72] Inventors [50] Field of Search 75/ 1 24, I25, I26, Machine Searched Nakazawa, Kawasaki-shl, all of Japan [56] keferencyes cied [21] Appl. No. 814,276 1 g v UNITED STATES PATENTS 1 Filed p 7 2,763,544 9/1956 Wagner 75/125 1 Patented K b Mk K sh 2,845,345 7/1958 Bauscher 75/125 [73] Asslgnee agz z z 8 us a a Primary Examiner-Hyland Bizot 9 o o I 32] Priority Apt 8, 1968 Anomey-Lmton & Linton [33] Japan [31] 43/2309 ABSTRACT: Corrosion resisting low alloy steel having stresscorrosion cracking resistability, good weldability and higher R 0s N R STING Low ALL Y STEEL strength under some kind of environment containing H 8 and [54] 52 g ig Fig 0 the like, which is chiefly composed of Cu-Cr-Al system constituents without addition of strengthening elements such as [52] HS. Cl 75/125, Ti b v and the m 40 A 0- 0- X V \J W 30 I k In A S WELDED) INVENTION I M A a 20 (rs-. B J 5 T5 EL HF comPRRlT/V STEEL l0 I I0 I00 200 RIJPTURE (A /t) STRESS (K 1) PATENTEDNBV 23 |97| 3,622 30s RIJPTURE (in) TOSHIO NBKAZH ATTORNEYS CORROSION RESISTING LOW ALLOY STEEL The present invention relates to economical corrosion re- It is well known that stress-corrosion cracking often occurs in some fields as in the petroleum industry. Accordingly, preventing oil well tubing, valves. bolts, nuts and the like, which are employed in oil fields containing H 5 gas. from outpointed out as under-mentioned. Upper limit of C content, i.e. 015%, is based on the fact that more than 015% C makes corrosion resistability and stress-corrosion cracking resistability worse and also deteriorates its weldability. 02% Si and 0.3% Mn is the lower limit content respectively for keeping sufficiently high yield point and tensile strength and more than 0.8% content of Mn deteriorates corrosion resistability or more than 0.6% content of Si increases the brittleness. The reason that P and S is limited to less than 0.03% respectively is break of the above stress-corrosion cracking, should be on account of accelerating stress-corrosion cracking. Cu is an further examined. As a matter of fact, reexamination on 9% Ni element of making the corrosion resistability increase and of steel and the like of which the above parts are made is actively raising the strength of the steel. However, the above effects indone and many studies as to how the composition exerts an incase of less than 0.2% content of Cu are impossible to attain fluence upon the quality of the parts and upon the occur- I 5 and more than 0.6% content of Cu brings about adifficulty of Fence-5 of grass-corrosion "inking has been announcedmanufacturing good steel and simultaneously results in injurevel" means of decisively Solving said P F ale not y ing stress-corrosion cracking resistability and weldability. Or esiablished and are more deciding of employed else shows good stress-corrosion cracking resistability with improved corrosion resistability. if the content of Cr is less than lt is an actuality that such a passive means as me 0.2% it is, however, difficult to expect the above efiects. More fibove forced to h f than l.0% content of Cr has had influence on both workability mg R s of the above f' steel a case pomt' and weldability of steel. A great quantity of Al, which is possisensb'my 2 above crackllfg m weldllfg place very ble to make said stress-corrosion cracking resistability of steel elevated l diff-cult to be f even If P heap improve, results in roughening the skin of ingot and lowering "eatmem carved f mem'oned W the yield, therefore, Al content is limited to less than 0.2%. the steel keeping resistability for said stress-corrosion A I cracking. which is owing to sulfide system inclusions in the The Steel based on the above-mentioned composition is welding place, is not yet found out. shown in the following table I. In the table, steel A, B, and C The features of the present invention are found in stand for the present invention and steel D, E, and F are some Cu-Cr-Al system composition of low alloysteel, which is i ofofdiltafy Sleels- TABLE 1 C Si Mn P S Cu Cr Al Y.P T.S El.

- Present Invention steal:

A 0. 00 0. 22 0. 50 0. 023 0. 016 0. 28 0. 48 0. 010 42. 5 61. 2 38 0. 23 0. 67 0. 018 0. 021 0. 30 0. 47 0. 015 33. ti 50. 3 38 0.34 0. 55 0. 022 0.022 0. 0.43 0.190 32. 3 50. ii 37 tr 0. 40 0.010 0.020 20.2 41. 47 0. 26 0. 02 0. 07s 0. 024 0. s0 0. 04 34. 0 40.0 as 0.38 1.18 0.022 0.020 31. 5 45. 37

chiefly comlmsed of to 05% to Cr and P to The above steels, table I, are immersed for 50 days into a (120% saturated solution by H 5 and CO gas and its corrosion cmi of V invention is Provide steel brittlement loss are investigated on the steel. Table ll shows having corrosion resistability, especially stress-corrosion these l cracking resistability under a kind of environment containing H 8 gas and the like. TABLE ll Another object of the present invention is to provide the V v Test Steel Corrosion embrittlement steel having a low cost and being able to make the corrosion m ing/cm, embrittlement loss reduce by about half in comparison with ordinary high-strength steel.

A further object of the present invention is to provide the The pmcm Q steel having higher strength in company with excellent corroinvcmhm and C u sion resistability without special strengthening elements, e.g. D |s.1 Ti Nb a d the Comparative steel E l2 Additional objects of the present invention will become F clear by the following description referring to the examples and the accompanying drawing in which;

The FIGURE is a graph Showing stress conosion cracking According to the above table ll, it is clearly understood that resistability of the present steel in comparison with ordinary the said corrosion embrittlement loss of this invention steels corrosion resisting steels. reduces by half in comparison with the comparative steels.

According to the present invention, the specified chemical And then, stress-corrosion cracking test is carried out on the composition, by weight percent, is as follows: above steels. These results are shown in the accompanying FIGURE. Referring now to the FIGURE, the strength of the 0 04 w 0 W7 C invention steel, after the above test, has been still kept at the 6,; high degree after 200 hours, which is about 40 kgjmmf. On 0.3 m 0.3% Mn the other hand, the strength of the comparative steel has P rapidly lowered to about 20 kg./mm.". It is evident that these 5? i results shows excellent properties of this invention steel under 03 m some kind of environment containing H 8 gas and the like.

F Al According to the present invention, it is, moreover, conbahn Ming impumie" firmed that proper heat treatment, e.g. quenching and temperl I A" ing treatment, is possible to be freely carried out on the in the present invention, the reason for which the chemical ground that some strengthening elements such as Ti, Nb, V

composition was determined mentionedabove should be and the like are not added to the steel.

0.04 to 0.15% C 0.20 to 0.67: Si

0.30 to 0.8% n

up to 0.03% up to 0.03% 02 to (H156 0.3 to LOK up to 0.20%

balance being Fe and unavoidable impurities.

2. Corrosion resisting low alloy steel as claimed in claim 1 wherein the content of Al is 0.01 to 0.19%. 

2. Corrosion resisting low alloy steel as claimed in claim 1 wherein the content of Al is 0.01 to 0.19%. 